Isares Dhuchakallaya

Numerical modelling of diesel spray auto-ignition and combustion

This work presents the development and implementation of a spray combustion model based on the spray size distribution moments approach to spray modelling. The governing equations for both the gas and liquid phases are solved by the finite volume method based on an Eulerian framework. The model used in the auto-ignition and combustion analysis is a combination of the probability density function and eddy break-up approaches. This scheme is developed in order to effectively validate both ignition and combustion phases. It is designed to compromise between the chemical reaction rate when dealing with the auto-ignition mode, and the turbulence reaction rate which dominates the combustion mode using a reaction progress variable which represents the reaction level. These average reaction rate source terms in transport equations for species are evaluated by a probability density function averaging approach. The developed ignition and combustion model is shown to have significant potential as a numerical tool for predicting the phenomena involved in spray combustion in diesel engines.

Effect of phase adjustment on the acoustic field of a cascade thermoacoustic engine

This study set out to explore the influence of phase adjustment on the acoustic field of a cascade thermoacoustic engine. The system consists of one standing wave unit and one traveling wave unit arranged in series. The straight-line configuration allows suppressing a time-averaged mass flow or Gedeon streaming, which causes some unwanted convective heat transport and reduces the efficiency of the system. Theoretically, the regenerator of the traveling wave unit must be operated within the traveling wave phasing and high impedance region in order to achieve an efficient performance. The various techniques of phase adjustment by modifying the configurations and geometrical dimensions of the system are investigated both numerically and experimentally to adjust the position of the sweet spot as well as to achieve the high acoustic impedance in the regenerator. The effective tuning methods with less modification here are accomplished by changing the volume of the down-cavity and reducing the flow area of the down-resonator by inserting the pencil. However, the pencil insertion scheme causes an extra loss due to viscous dissipation that should be taken into account. The change of the down-resonator length has a strong effect on the acoustic field in the system. After the phase-adjustment schemes are completely implemented, the performance of the proposed system is significantly improved, in which the regenerator of the traveling wave unit operates within the traveling wave phase region with high acoustic impedance. This prototype operated with air at atmospheric pressure can supply acoustic power up to 33 W to the down-resonator, which is about 9.5% of Carnot efficiency.